The present invention relates to preventing the clogging of ink jet nozzles in ink jet printers, particularly when those printers have been off for an extended period of time.
Ink jet printers, which are currently in use, are fast, relatively noiseless and provide a resolution of approximately 1000 adjacent dots per line. In order to provide the necessarily fine ink particles, the ink jet nozzles must be correspondingly small. The small diameter of the nozzle, together with the small volume of ink in the nozzle awaiting ejection creates a problem wherein the ink within the nozzle may at least begin to solidify when exposed to room atmospheric conditions. If the time between ink ejections exceeds 15-30 minutes, depending on the type of ink and the inner diameter of the nozzle, the ink may begin to solidify and thus prevent the ejection of the proper amount of ink when the print command is received by the ink jet nozzle subsystem. If this occurs, the line printed will at least be incomplete. If the ink nozzles become clogged, they are not easily cleared and an expensive service call may result because of the small size of those nozzles.
Several techniques have been used in prior art ink jet printers to clear an ink clog in a nozzle or to minimize the possibility of the clogging of the ink nozzles. The Silonics Model 30790-02 ink jet printer, during normal printing, utilizes the microprocessor to monitor the number of drops each ink channel ejects. If a channel has not been used within a 100 second period, the microprocessor commands the channels to eject a drop of ink.
U.S. Pat. No. 3,925,789 discloses an ink jet printer wherein, during normal printing, a timer is employed to count the elapsed time between ink ejections from each of the ink nozzles. Then, if the elapsed time between ejections for any one nozzle exceeds a preselected time, e.g. 15 to 30 minutes, the control unit is triggered which in turn activates the ink pump to cause ink to be ejected from the unused nozzle into an ink collector for 10-12 seconds. In addition, this patent discloses the ejection of ink from each nozzle for several seconds upon the application of power to the printer. This is intended to dislodge a clog from the ink nozzles which may have developed while the printer was turned off. If the printer was off for an extended period this method may not be able to dislodge a well hardened clog.
A technique used in other ink jet printers to minimize the possibility of the development of clogs is the washing of the nozzles after each copy is completed. After each copy is completed the ink nozzles are transported to a home position where a wash station, including a water tight rubber seal, is brought into communication with each nozzle. Water from a wash tank is then sprayed on the external portions of the nozzles to remove any ink residue which may have collected on the external portion of the nozzle in the vicinity of the open end of the nozzle. This water is then returned to the tank. During the power off period the nozzles remain sealed with the wash station where the humidity is slightly higher than in the ambient room environment. However, even under the elevated humidity conditions the ink remaining within the ink jet nozzles will harden and clog them after a few days.
None of the above discussed prior art approaches for the preventing of clogs within the nozzles of ink jet printers provide a positive method for preventing clogs when the printer is not powered for extended periods of time. The present invention provides a method for preventing the clogging of the ink nozzles when the printer is not in use for an extended period without having to drain and flush the ink subsystem, including the nozzles.